Process for the production of esters of allyl-brominated olefinic alcohols



United States Patent PROCESS FOR THE PRODUCTION OF ESTERS OF ALLYL-BROMINATED OLEFINIC ALCOHOLS Hermann Schaltegger, Flamatt, Bern, Switzerland No Drawing. Application August 11, 1954, Serial No. 449,270

13 Claims. (Cl. 204158) The present invention relates to a process for the u-position to the olefinic double bond.

In my United States patent application Serial No. 114,691, filed September 8, 1949, now Patent No. 2,647,867, and in my copending application Serial No.

, preparation of esters of olefinic alcohols brominated in 220,344, filed April 10, 1951, now abandoned, it has been proposed to introduce free bromine in the a-position to an olefinic double bond of certain types of organic compounds at low or relatively moderate temperatures. It has now surprisingly been found that it is also possible to prepare in a corresponding manner esters of unsaturated alcohols brominated in u-position to a double bond thereof. Such bromination has proved possible not only for the esters of acyclic but also for those of cyclic unsaturated alcohols. The use of the esters instead of the free alcohols is necessary because the free hydroxyl group of alcohols would be disturbing in said brominating reaction. The simple carboxylic acids, such as acetic acid, are best suited for this purpose.

It is therefore, an object of the present invention to produce esters of unsaturated alcohols brominated in u-position to the double bond.

It is another object of this invention to produce esters of unsaturated alcohols brominated in a-position to the double bond by direct reaction of the start materials with free bromine. I And it is a further object of this invention to efiect direct bromination of esters of unsaturated alcohols in Deposition to the double bond at relatively low or moderate temperature.

' Other objects and advantages of this invention will 1 become apparent from the following specification and the annexed claims.

7 With these and other objects in view, the process in accordance with my present invention essentially is as follows:

Esters of unsaturated alcohols are dissolved in nonpolar solvents indifierent against halogen. The choice of '-'"-solvents useful for this purpose is not very great, and

from a practical point of view carbon tetrachloride and carbon disulfide are those which are here to be considered. The other non-polar solvents indifferent against halogen either have boiling points which are by far too low for their use in technically carrying out the present process in a simple manner, or their boiling points are so high (over 100. C.) that secondary decompositions Patented Apr. 30, 1957 dilute state, either in the form of a solution in an indifferent solvent or in mixture with an indilferent gas. Further-on it is advantageous to add the dilute bromine only gradually to the solution of the esterified unsaturated alcohol. This gradual addition is preferably carried out by means of inlet pipes the openings of which are deeply immersed into said solution under treatment so that said dilute bromine is quickly spread or divided within the reaction solution. Additionally, this solution may be stirred for still better and intimately mixing the reactants.

The construction of the apparatus to be used for carrying out the process may vary in many respects, particularly according to the details of carrying out the process. For example, the bromine may be added to the reaction solution in vapor form mixed with an inert gas, such as nitrogen. It is possible during the reaction to heat the reaction liquid to boiling under reflux or, still better, to distill under lightly diminished pressure during the reaction part of the solvent together with the hydrobromic acid forming.

During the entire reaction, the reaction vessel has to be irradiated, because otherwise saturated dibromo derivatives are formed instead of the unsaturated allyl brominated compounds desired. Any type of light sources of the commerce, or else, may be employed for this purpose, such as glow lamps, fluorescent lamps, quarts lamps, and so on.

The reaction time or period of the bromine addition to the ester solution has practically proved to be best between about 40 to minutes. It would theoretically be more advantageous to add the bromine still more slowly. However, the esters of the allyl brominated alcohols to be produced are very sensitive to temperature and decompose after some time already at about 80 C. and, for this reason, the reaction time must not be too long if an optimum of unsaturated allylic brominated compound is to be obtained.

Of the bromination products obtained, only those of simple structure and of comparatively low molecular weight can be distilled in vacuo without decomposition. For approximately determining the yield, the hydrobromic acid formed during the bromination was titrated. According to the equation of the reaction, one mol of hydrobromic acid is to be formed per mol of allylic bromined. The number of hydrobromic acid mols thus indicates the so-called degree of the substitution.

The following reactions may yet be named as additional proof for the presence of bromine in the allylic position: A precipitation of silver bromide is immediately formed by addition of an alcoholic solution of silver nitrate. This reaction is not obtained with normal aikyl bromides. Only a slight cloudiness is to be observed in this case, as is well known, after boiling the solution for a long time with a solution of silver nitrate. Finally, it is possible to add bromine under irradiation to the unsaturated allylic monobromic product dissolved in ether or acetic acid, whereby a saturated tribromo alcohol is obtained and may be separated, showing that a double linkage was present in the originally produced allylic bromide.

My present process makes it possible to produce a very large number of esters of different unsaturated alcohols brominated in the allyl-position. Generally spoken esters of all such unsaturated alcohols may be brominated in the allyl-position which contain at least one -O=CC 1H I I I group in their molecule. Some examples of such alcohols are: crotyl or crotonyl alcohol, 2-pentenol ('y-ethylallyl alcohol), methyl-propenylcarbinol, 3-hexeno1, isopropyl r 3 isocrotyl-carbinol, 2-decene-7-ol, linalool, citronellol, farncsol, oleyl alcohol, phenylcrotyl, alcohol, terpinol, pulegol verbenol, and so on. All these alcohols are best used in the form of their acetates.

will distil off with the solvent. This can easily be achieved by a suitable arrangement of the gas-inlet pipe and suitable regulation of the distilling velocity of the carbon tetrachloride. After finishing the bromination, the carbon tetrachloride still present is evaporated in vacuo. The

Example 1 5 residue is a yellowish oil which somewhat fumes at the 11.4 grof crotonyl acetate boiling at 126128 C. under air and shows a bromine content of 19.4% (calculated a pressure of 715 mm. Hg are dissolved in 800 cc. of for the rnonobromide is 20.5%). A precipitation is carbon tetrachloride in a cylindrical glass vessel of a formed at once by silver nitrate.

Examples 3-6 Yleldin Mono- Period bromo- Worked Acetate (g.) in Bromine (g.) in of olefinic as in Acetateused of Solvent (00.) Solvent (00.) Irradi- Alcohol or Example ation Degree or Substitutlons, percent oleyl alcohoL- 16/900 C014 8.1/500 C014 52' 76 oitronellol 20/1,000 Gs, 16 7000 45' 51 geraniol 20/l,000 00h 16Br :N=1:20 55 48 terpinol 19.711.200 Coin-.- 16/200 0014 40' 01 capacity of about 2 liters and a diameter of about 10-12 Numerous modifications and variations of the process cc. The cover is provided with a passage for a stirrer, described may be devised Without departing from the two calibrated dropping cylinders of 200 cc., each, and principles and the true spirit of the invention, and no a genufiected outlet pipe connected with a descending other limits should be imposed thereon than are indicated condenser. The glass vessel is uniformly irradiated at in the annexed claims. all sides by four ZOO-watt lamps. The inlet pipes for This application is a continuation-in-part of my cothe bromine immerse into the solution and end near the pending application, Serial No. 220,344, filed April 10, bottom of the vessel. It is suitable to make use of inlet 1951, now abandoned. pipes perforated like a fine sieve in order to obtain good What I claim is: distribution of the bromine. The recipient of the con- 1. A process for the production of esters of olefinic denser is connected with a suction pump of the type alcohols selected from the group consisting of acyclic working by streaming water, whereby the distillation and monocyclic olefinic alcohols brominated in tat-position velocity can be regulated by control of the sub-pressure. to the olefinic double bond comprising treating dilute The carbon tetrachloride solution is heated to boiling, solutions containing not more than 2% of esters of oleand 16 g. of bromine dissolved in 400 cc. of carbon tetrafinic alcohols having at least one double bond in the chloride are allowed to drop into said boiling solution molecule and selected from the group consisting of from the two dropping cylinders in such a degree that acyclic and monocyclic olefinic alcohols with free bromine 50 minutes will be required to introduce the entire amount while irradiating the reaction mixture with light, and or" said bromine solution. Stirring is performed during separating the resulting olefinic bromo-esters by evaporathe bromination, and the velocity of the distilling-off is tion of the solvent employed. regulated so that just the same amount of solvent is dis- 2. A process in accordance with claim 1, wherein the tilled off as is added by the bromine solution. The hydrobromine, too, is employed in a dilute state. gen bromide formed in the bromination is removed with 3. A process in accordance with claim 2, wherein the said solvent. After the above named period of time, bromine is dissolved inthe same type of solvent as the the remaining carbon tetrachloride is distilled off in vacuo, material under treatment. and 20 g. of brominated crotonyl acetate are obtained. 4. Aprocess in accordance with claim 2, wherein the A sudden precipitation of silver bromide is formed by adbromine is diluted by an indifferent gas. dition of an alcoholic silver nitrate solution to a sample 5. A process in accordance with claim 4, wherein the of the resulting product. The bromocrotonyl acetate is inert gas is nitrogen. somewhat fuming in the air. The bromine content of 6. A process in accordance with claim 1, wherein a said compound corresponds to that of a monobromide. relativey low boiling inert non-polar solvent is employed. Emmple 2 A process in accordance with claim 1, wherein the hydrogen bromide formed during the reaction is con- 32 g. of olcyl acetate are dissolved in 120 cc. Of tinuously removed from the reaction solution by distillacarbon tetrachloride and the solution is uniformly irti together i h solvent vapors, radiated by four 22-watt lamps. The reaction vessel is 8. A process in accordance with claim 6, wherein the pml'idcd with a dislributer for g (P glass P p 50 treatment of the dilute solution of said olefinic coma or the l a descending condenser, and a pound under treatment with bromine is carried out at a stirrer. The solution is heated to gentle boiling While d t temperature not hi h h that f the boiling Surfing, and mixtbre of about 19 Parts y Volume 0f point of the relatively low boiling non-polar solvent. bI'OmiP-C and about 290 Paris y Volume of nitrogen 15 9. A process in accordance with claim 1, wherein the lbw gradually mtrbduced into the Slightly boiling Sohlbromine is added gradually to the dilute solution of Within 55 Tbe Vapor P ssure of the said olefinic compound under treatment and only in bfofbillejgs separator 18 l'bgblated $0 p y such a degree that side-reactions by the presence of c g 1! nto ced water) K g- 0f fic e excess bromine in the solution are avoided. mile-(lubed during 581d Pefwd o the solution to be 10. A process in accordance with claim 1, wherein the Nom nated. The hydrogen bromide forming in this d lut l ti f id l fi i compound to be reacted bromination lS continuously driven offduring the entire upon by the bromine contains. about 1 to 2% of said treatment together with-evaporating carbon tetrachloride. olefinic compound under treatment. The introduction of the bromine-nitrogen mixture and the 11. ;A process in accordance with claim 1, wherein the (1151111111905 0f SOIVeHt are to be tuned Wlth r spec t said dilute solution isstirred during the treatment with each other in such a manner that no unused bromine bromine.

12. A process for the bromination of an ester of an ethylenically unsaturated alcohol selected from the group consisting of acyclic and monocyclic alcohols, said bromination to be effected in u-position to the double bond, comprising the steps of dissolving said ester in a relatively low boiling inert non-polar solvent to form a solution having a concentration of not more than about 2%, maintaining said solution at the boiling point of said solvent, gradually introducing bromine into said solution While irradiating the solution With light, simultaneously withdrawing hydrobromic acid as formed in the course of the reaction, and separating the ester of said alcohol brominated in a-position to the double bond.

13. The process which comprises forming a solution containing not more than about 2% of crotonyl acetate dissolved in a solvent selected from the group consisting of carbon tetrachloride and carbon disulfide, boiling said 6 solution, gradually introducing bromine into said solution while irradiating the solution with light, simultaneously withdrawing hydrobromic acid as formed in the course of the reaction, and separating from the solution crotonyl acetate brominated in tat-position to the double bond.

References Cited in the file of this patent UNITED STATES PATENTS 2,531,688 Jones et al Nov. 28, 1950 2,554,533 Ladd May 29, 1951 2,585,998 Buisman Feb. 19, 1952 2,590,637 Miescher et al. Mar. 25, 1952 2,633,451 Schaltegger Mar. 31, 1953 2,647,867 Schaltegger Aug. 4, 1953 

1. A PROCESS FOR THE PRODUCTION OF ESTERS OF OLEFINIC ALCOHOLS SELECTED FROM THE GROUP CONSISTING OF ACYCLIC AND MONOCYCLIC OLEFINIC ALCOHOLS BROMINATED IN A-POSITION TO THE OLEFINIC DOUBLE BOND COMPRISING TREATING DILUTE SOLUTIONS CONTAINING NOT MORE THAN 2% OF ESTERS OF OLEFINIC ALCOHOLS HAVING AT LEAST ONE DOUBLE BOND IN THE MOLECULE AND SELECTED FROM THE GROUP CONSISTING OF ACYCLIC AND MONOACYCLIC OLEFINIC ALCOHOLS WITH FRE BROMINE WHILE IRRADIATING THE REACTION MIXTURE WITH LIGHT, AND SEPARATING THE RESULTING OLEFINIC BROMO-ESTERS BY EVAPORATION OF THE SOLVENT EMPLOYED. 